This invention relates in general to a fusing assembly for an electrostatographic reproduction apparatus, and more particularly to an electrostatographic reproduction apparatus fusing assembly, which includes a pre-heater.
In typical commercial reproduction apparatus (electrographic copier/duplicators, printers, or the like), a latent image charge pattern is formed on a uniformly charged charge-retentive or photoconductive member having dielectric characteristics (hereinafter referred to as the dielectric support member). Pigmented marking particles are attracted to the latent image charge pattern to develop such image on the dielectric support member. A receiver member, such as a sheet of paper, transparency or other medium, is then brought into contact with the dielectric support member, and an electric field applied to transfer the marking particle developed image to the receiver member from the dielectric support member. After transfer, the receiver member bearing the transferred image is transported away from the dielectric support member, and the image is fixed (fused) to the receiver member by heat and pressure to form a permanent reproduction thereon.
One type of fusing device for typical electrographic reproduction apparatus includes at least one heated roller, having an aluminum core and an elastomeric cover layer, and at least one pressure roller in nip relation with the heated roller. The fusing device rollers are rotated to transport a receiver member, bearing a marking particle image, through the nip between the rollers. The pigmented marking particles of the transferred image on the surface of the receiver member soften and become tacky in the heat. Under the pressure, the softened tacky marking particles attach to each other and are partially imbibed into the interstices of the fibers at the surface of the receiver member. Accordingly, upon cooling, the marking particle image is permanently fixed to the receiver member.
Certain reproduction apparatus recently introduced into the market have been designed to produce multi-color copies. In such reproduction apparatus, multiple color separation images are respectively developed with complementary colored marking particles, and then transferred in superposition to a receiver member. It has been found that fixing of multi-color marking particle images to a receiver member requires substantially different operating parameters than fixing standard black marking particle images to a receiver member. Moreover, the respective operating parameters may in fact be in contradistinction. That is, multi-color images require a high degree of glossiness for a full, rich depth of color reproduction; on the other hand, since glossiness for black marking particle images may significantly impair legibility, a matte finish is preferred.
It is known that the glossiness of a marking particle image is, at least in part, dependent upon the marking particle melting characteristics in the fixing process. In general, the fixing apparatus serves to soften or at least partially melt the marking particles, enabling the marking particles to permeate into the fibers of the receiver member so that the marking particles are fixed to the receiver member to give a glossy image reproduction. For example, the fixing apparatus may include a heated roller which contacts the marking particles and the receiver member. With multi-color marking particle images, the multiple color marking particle images are respectively melted and fixed by the heated roller. If the color marking particle images are not sufficiently melted, light scattering cavities may occur in the copy which degrades the color reproduction. Moreover, if the marking particles on the receiver member do not have a mirror-like surface, incident light is reflected by diffusion from the marking particle surface and is not admitted into the marking particle layers, making the colors on the receiver member appear dark and cloudy. Therefore low melting point marking particles are used. They yield few cavities and a hard flat surface so as to give glossy and vivid colors in the reproduction.
Low melting point marking particles are subject to increased image offset to the heating roller. This can produce undesirable defects in the reproduction or subsequent reproductions. Although image offset can be reduced by application of fusing oil to the heating roller, the use of such oil introduces further complications into the fusing system, such as handling of the oil and making sure that the layer of oil on the roller is uniform. Alternatively, a mechanical arrangement for reducing image offset, without the need for fusing oil, has been found. Such mechanical arrangement provides an elongated web which is heated to melt the marking particles and then cooled to cool the particles and facilitate ready separation of the receiver member with the marking particle image fixed thereto from the elongated web. The nature of operation of the elongated web arrangement also serves to increase the glossiness of the fixed marking particle image. As a result, such arrangement is particularly useful for multi-color image fusing, but is not particularly suitable for black image fusing.
In color electrophotographic reproduction apparatus, generally using a nip forming roller fusing, it has been found that an increase in fusing roller speed, facilitates the matching of image-gloss to paper-gloss, and also serves to reduce differential gloss. U.S. Pat. No. 5,521,688 (issued May 28, 1996) describes a radiant oven prior to two pairs of glossing rollers. The radiant oven fixes the marking particles (resulting in a matte image), and then increases the gloss by heat and pressure while passing through the glossing rollers. Without the use of a pre-heater, fusing speed generally limited, and there is thus a limited capability to match image gloss to paper gloss. Other patents describing pre-heating systems in electrophotographic fusers include U.S. Pat. No. 4,959,529 (issued Sep. 25, 1990); U.S. Pat. No. 5,784,679 (issued Jul. 21, 1998); U.S. Pat. No. 5,412,459 (issued May 2, 1995); and U.S. Pat. No. 4,071,735 (issued Jan. 31, 1978).
This invention is directed to a pre-heater for a reproduction apparatus fusing assembly which utilizes hot-air impingement to transfer heat to an image-wise marking particle pattern on a receiver member. The pre-heater includes a housing defining a heating chamber. The heating chamber defines an opening adjacent to the receiver member travel path. A heating element is located within the housing. An airflow system is provided including a blower, and a distribution plenum in flow communication between the blower and the heating element. An impingement member is positioned in the chamber opening adjacent to said travel path. An impingement plenum is in flow communication between the heating element and the impingement member, and a return conduit is in flow communication between the opening and the blower. Accordingly, air from the blower is delivered through and heated by the heating element, impinges upon a receiver member bearing a marking particle image in the opening, and is returned to the blower while being prevented from escaping from the chamber.
The invention, and its objects and advantages, will become more apparent in the detailed description of the preferred embodiment presented below.